Well perforator



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Patented Aug. 10, 1948 WELL PERFORATOR Robert F. Davis. Falls Church,Va., assgnor to Well Surveys, Incorporated, Tulsa, Okla., a corporationof Delaware Application July 19, 1946, Serial No. 684,761

4 Claims. (Cl. 164-05) This invention relates to an improved method andapparatus for firing a projectile into the wall of an oil well or otherdrill hole. More particularly it relates to a method and apparatus forring a projectile through a steel well casing to provide an openingbetween the interior of the well casing and the surrounding geologicalstrata.

Prior to this invention it has been an established practice to provideopenings branching off from a well bore intermediate its ends by iiringprojectiles radially from the well bore into the surrounding strata. Inmost instances, this is done to provide an opening through a steel wellcasing. but in some instances it may be done merely to provide anopening extending radially from an uncased well.

In most instances wells are illled with liquid and this necessitates thefiring of the perforating projectile beneath the surface of the liquidwhich illls the well. In many instances it is desired to iire theperforating projectile into the wall of the drill hole at a distanceseveral thousand feet from the surface of the earth and several thousandfeet below the surface of the liquid in the drill hole.

Under such circumstances a maior diiculty is always encountered in thatitis necessary for the projectile to move a certain amount of thesurrounding liquid out of the way before it can reach and penetrate thewall of the drill hole. Since liquid is practically incompressible, thisnecessitates the movement of liquid all the way to the surface of theliquid in the drill hole. As this often means the movement oi' aconsiderable body of liquid, the inertia of the liquid due to its weightmakes extremely ditilcult the rapid acceleration of the projectile.Hence. in normal operation, the projectile is very considerably sloweddown by this phenomena and the penetration into the wall of the drillhole is not nearly so deep as it otherwise would be.

A further diiliculty is encountered whenother equipment is in the drillhole at the time the per-- foration is to be accomplished. For example,it is often highly desirable to lower a well exploring' unit with theperforator so as to locate the strata into Which it is desired to sendthe perforating projectile. Such an exploring device may be one of thetype described in Technical Publication No. 193 of the AmericanInstitute of Mining vand Metallurgical Engineers (February 1945) andentitled Some practical aspects of radioactivity well logging, by WarrenJ. Jackson and John L P. Campbell.

When such a. device is lowered into a well along with a perforator andthe perforator is then red,

2 a violent shock wave progresses through the liquid in the drill holeand is quite likely to damage the sensitive well logging instrument,particularly if it is anywhere near the perforator.

The purpose of the present invention, therefore. is to increase theeffectiveness of perforating projectiles in perforating the well casingand the surrounding strata, and at the same time to avoid the eiects ofa violent shock wave on nearby sensitive equipment.

Briefly the present' invention comprises burning a quantity of slowburning powder at a point adjacent the place where the 'projectileemerges from the barrel from which it is ired, and then before the gasformed by the burning ol the slow burning powder can leave the area.exploding the charge which propels the projectile, so that theprojectile will not be forced to displace a large quantity of liquid andwill not generate a shock wave extending throughout the uid in the drillhole.

Since the propellent charge for the projectile is normally ignited byelectrical means, it is a relatively simple matter to ignite both theslow burning charge and the propellent charge by the same electricalmeans and to insert a time delay circuit in series with the igniter forthe propellent charge so that there will be the necessary delay betweenthe time the slow burning 'charge is ignited and the time that thepropellent charge is ignited.

Further details and advantages of this invention will be apparent fromthe appended drawing, and the following detailed description thereof.

In the drawing, Figure 1 is a vertical crosssection of a part of a caseddrill hole and a gun perforating device in which are embodied theprinciples of this invention; and

Figure 2 is a vertical cross-section of a part o! a cased drill hole inwhich is positioned a gun perforator and a well-exploring device inaccordance with this invention.

As illustrated in Figure 1. the drill hole consists of a well casing l0embedded Iin surrounding earth ii and containing a. gun perforatingdevice i2 (shown only in part). Normally, such a. well casing will beillled with liquid to a level far above the point at which it is desiredto peri'orate.

The gun perforator illustrated consists of an outer casing I3 in whichis mounted a gun barrel 'I4 which in turn contains a perforatingprojectile I5 and a propellent charge I6, which when exploded will drivethe perforating projectile IB through the well casing I 0 and into thesurrounding strata.

In accordance with' this invention, a slow burnlng powder charge i1 isplaced just ahead of the perforating projectile i5 and a detonatorcircuit I8 is connected so that upon operation it causes the slowburning powder charge l1 to be ignited. The propellent charge I6 is alsoconnected to the detonating circuit I8 but instead of being connecteddirectly, the propellent charge is connected through a time delaycircuit I9 which has a time constant such' that the propellent charge i6will not be red until sufficient time has elapsed for the slow burningcharge I1 to burn and forma gas pocket adjacent the forward end of theprojectile.

The slow burning powder or charge -can be oi. any desired material thatwill burn slowly and `produce a considerable volume of gas Withoutcausing any abrupt pressure increase in the well or any appreciableshock wave. 'I'he time delay circuit -I9 may be of any desired type. theonly requirement being thatv it produces sufcient delay between theilring of the slow burning charge and ythe firing of the propellentcharge. A slow burnlngpowder fuse may even be substituted for the timedelay circuit to produce the same result.

The construction of the gun perforat-or casing, the gun barrel, theprojectile and the propellent charge is conventional, except that itusuallyT is desirable to so form the gun barrel that an annular ring isformed around the propellent charge, which-ring serves to prevent theprojectile from being forced backward against the propellent charge whenthe slow-burning powder charge is fired. This avoids any possibility ofthe pressure from the slow-burning powder charge being transmitted'through the projectile and causing -detonation of the propellent chargesooner than desired` The 'slow burning powder` charge need notnecessarily be placed in the gun barrel but may be placed in a separatechamber near the gun barrel an-d this chamber may be vented eitherintothe 4gun barrel or into the well at a point .near the gun barrel; Itis desirable, but not essential, that the liquid in the gun barrelimmediately ahead of: the projectile be blown out by .the slow burning.powder charge before the propeilent charge is ignited. The desirableresult Vwill bep'ar-tially realizedA even if the gas formed .by the slowburning powder charge is at some little distance from the gun barrel,when the explosion occurs. -It is desirable, however, that the slowburning powder charge clear the barrel and the surrounding area and thatall be clear of liq- .uid at the time the propellent charge is ignited.

i In many instances it is desirable to accurately I position theperforator by the use of a well surlveying instrument suspended on thesame cable from the surface of the earth. In order to positionvthe-periorator accurately itis desirable that ,the surveying instrumentbe positioned relatively close to the perforator.

. Following the principles of this invention and .as illustrated inFigure 2, a well surveying Ilnstrument 30 may conveniently. be suspendedfrom the same cable 3| and positioned a short distance above aperforator 32. The gas formed by the slow burning powder charge willthen act to absorb the shock wave produced by the explosion of thepropellent charge and avoid damage to th surveying instrument.

A protecting disk may be placed between the slow-burning powder chargeand theouter end of the gun barrel as shown in United States Patent2,029,454, granted February 4, 1936, to Walter T. Wells.

What is claimed is:

1. A method of perforating the wail of a drill hole that comprisesigniting a charge of slow burning powder in a drill hole adjacent theplace where the wall is to be perforated and immediatelythereafter,before the gas formed by the slow burning powder has had a chance toleave the area, firing a projectile into the wall of the drill hole atthe place where the drill hole is to be perforated.

2. A perf'ora-tor for the wall of a drill hole that comprises a capsuleadapted to be lowered into a drill hole, a radially directed gun barrelin said capsule, a projectile in said gun barrel, a propellent chargebehind said projectile, a slow burning powder charge adjacent theforward end of said projectile and means to detonate said slow burningpowder charge and said propellent charge sequentially and atpredetermined intervals of time.

3. Apparatus for perfora-ting the wall of a drill hole that comprises anexploring device and a gun -p-erforator suspended from a single cableone above the other, said gun perforator including a slow burning powdercharge vented into the area surrounding the perf orator and means to rethe slow burning powder charge at a predetermined interval of time priorto the iiring of the propellent charge for the projectile.

4. A gun perforator for perf-orating the wall of a drill hole thatcomprises a capsule adapted rto be lowered into a drill hole, aprojectile in said capsule, a propellent charge arranged to propel theprojectile into the surrounding strata,'a slow burning powder chargepositioned adjacent the point where the projectile emerges from thecapsule and means to electrically ignite lsaid slow burning charge andsaid propellent charge, said means including a time delay circuitconnected to delay the ignition of the propellent charge until .a chanceto burn.

the slow burning charge has been ignited and had ROBERT F. DAVIS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,029,478 Haines Feb. 4, 19362,246,542 Slnth June 24,-1941

